There has conventionally been proposed a magnetic rotating apparatus having a stator in which a plurality of cores with winding are disposed at regular intervals along the circumferential direction and a rotor in which a plurality of permanent magnets are disposed at regular intervals along the circumferential direction and which rotates facing the stator (Japanese Laid-open Patent Publication Nos. 2006-187080 and 2009-118705, and WO 2009/060544).
For example, a magnetic rotating apparatus is disclosed in Japanese Laid-open Patent Publication No. 2006-187080. In the magnetic rotating apparatus, a variety of pulse currents are applied to windings when a rotor is in regions corresponding to different rotational position so that a repulsion force is generated between a permanent magnet and an electromagnet due to a winding.
A magnetic rotating apparatus is disclosed in Japanese Laid-open Patent Publication No. 2009-118705. The magnetic rotating apparatus is provided with a rotor made up of a plurality of permanent magnets disposed in the circumferential direction and a stator made up of a plurality of electromagnets disposed in the circumferential direction. Currents are applied to the electromagnets intermittently; thereby the rotor is rotated with an attraction force and a repulsion force between the permanent magnet and the electromagnet. According to the technique disclosed in Japanese Laid-open Patent Publication No. 2009-118705, the number of permanent magnets and the number of electromagnets are different from each other, so that a detent torque (cogging torque) is reduced.
A one directional electrification-type brushless DC motor is disclosed in WO 2009/060544. The brushless DC motor has a rotor which is rotated to function as a motor, and an AC voltage output winding which generates power directly by the rotation of the rotor.
Such a magnetic rotating apparatus is used to constitute an electric motor or a generator. For example, a rotational torque is developed by an attraction force or repulsion force between a permanent magnet and a magnetic field of a core by a current flowing through a winding, which makes it possible to function the magnetic rotating apparatus as an electric motor. An external rotational force is used to rotate a rotor, and the permanent magnet is rotated to change flux in the core to take out a current from the winding, which makes it possible to function the magnetic rotating apparatus as a generator.
The electric motor and the generator constituted by the magnetic rotating apparatus are coaxially formed to implement a motor generator.
In the magnetic rotating apparatuses disclosed in Japanese Laid-open Patent Publication Nos. 2006-187080 and 2009-118705, however, a large detent torque is caused. This is a factor that lowers the efficiency.
The brushless DC motor disclosed in WO 2009/060544 reduces a detent torque to some extent; however, this is not enough.
Further, when this type of magnetic rotating apparatus starts up as an electric motor, a temporary backlash (reverse rotation) occurs, which sometimes impedes a smooth start-up.